Feromoni e attrazione sessuale nei vertebrati

Pheromones are defined as conspecific chemicals which are secreted by an individual called the sender and evoke a change in the behavior and in the physiology of the other individual which is the receiver. Animals use pheromones for many forms of social interactions, such as reproduction, aggression, migration and signaling danger. Pheromones are detected by the vomeronasal organ which is part of accessory olfactory system.Vomeronasal receptors are divided in two classes: V1Rs and V2Rs. V1Rs are part of rhodopsin-type GPCR family and are involved in detecting small molecules like volatile compounds and steroids derivatives. In mice V1Rs recognize urinary molecules that convey information about sex and physiological states. V2Rs belong to C GPRC family and are involved in detection of large molecules like peptides and proteins.V2Rs receptors detect ESPs (exocrine gland-secreting peptide) ligands,like ESP1 secreted by extra orbital lacrimal gland of male mice and enhances female sexual receptivity. MUPs (Major Urinary Proteins) are ligands implicated in territorial demarcation and individual recognition.Pheromone behaviors depend on sex experience and internal state of the receiver.In the moment when a male detects another male MUPs or ESP1 pheromones it leads to aggressive behavior in order to show dominance and competition.On the other hand the final social behavior in female mice, is modulated by the hormonal state of female.During estrus, when the estrogen levels are high, the female responds to male pheromones with lordosis, sexual receptivity; meanwhile, during diestrus when the progesterone levels are high, female mice are indifferent to male hormone.Female mice respond with aggressive behavior towards male pheromones during motherhood, when the progesterone surges. After a successful reproduction, it is important for female mice to remember the chosen partner by memorizing his pheromones. Arc protein which is encoded by activity-regulated cytoskeletal Arc gene, is expressed in the cortical and hippocampal glutamatergic neurons. It is implicated in learning, memory consolidation and behavior. Localizations pheromones involves the integration of multiple sensory modalities, including the olfactory and somatosensory systems.To understand the implication of olfactory system and somatosensory sytem female mice were trained on a multimodal task in order to locate pheromones, by sampling volatiles from male urine through the orifices of varying dimension or shapes.In the experiment of multimodal learning of pheromone locations female showed a prefernece toward male urine scent compared to neutral stimuli water. When tested for memory formation 15 days after training the female mice were able to memorize the location of opposite sex pheromones.The memory was not formed when the somatosensory inputs of whisker pad where blocked,also it resulted on a lack of memory formation when the pheromonal cues were replaced with female stimuli.There was no evidence of memory formation on day 30 of memory testing.The association between olfactory and somatosensory systems was confirmed by the enhanced expression of the activity-regulated cytoskeleton protein on specific brain circuits during the day 15 of memory formation.